Torque-limiting device and farm machine using same

ABSTRACT

A torque-limiting device for secure transmission of a rotation between an inlet baseplate and an outlet baseplate, including at least one drive bolt that forms a breaking element by shearing in case of a torque exceeding a predetermined threshold, and an intermediate baseplate that is driven by the inlet baseplate and driving the outlet baseplate. The bolt ensures driving of the intermediate baseplate and the inlet baseplate or the outlet baseplate. The intermediate baseplate includes a locking element by shape cooperation with a locking part of the bolt. The intermediate baseplate is formed by two plates pressed against one another, one of which is used for housing of the locking part of the bolt and the other of which is used for axial support of the locking part and housing of the screw rod. An agricultural machine can include such a device.

The present invention relates to the field of agricultural machines andrelates on one hand to a torque-limiting device, in particular whereofthe breaking element shears, and on another hand to an agriculturalmachine, in particular a harvesting machine, in particular a machine forcutting and conditioning plants such as grass or forage plants.

In this field, harvesting plants consists essentially on one hand ofcutting them, and on another hand of conditioning the cut strands tooptimize the windrow, in particular its drying. The cutting is doneusing a cutting unit comprising cutting rotors bearing rotary knives,the cutting rotors rotate around a substantially vertical axis and aremounted next to one another. The conditioning is done by a conditioningunit placed downstream from the cutting unit, and essentially includingone or several conditioning rotors. The latter for example include aplurality of blades, fingers or flails, mounted pivoting around ahorizontal axis, transverse to the direction of advance of the machine,distributed angularly in parallel vertical planes, aligned along one orseveral shafts, so as to form a conditioning assembly.

In one configuration in the form of a pulled machine, the setting inmotion both of the cutting unit and the conditioning unit takes placefrom a coupler head connected to a tractor, driven in rotation by thetractor itself and driving a counter shaft extending in a drawbarwhereof the rear end is articulated to a chassis supporting the twounits, the shaft in turn driving a third shaft ending approximately at alateral end of these two units.

The cutting unit is traditionally set in motion by the third shaft usinga gear placed between them, which drives the first cutting rotor, and byestablishing driving of the successive cutting rotors between them, forexample a geartrain positioned below the cutting rotors. Theconditioning unit is for its part set in motion by a transmissiongearbox, extending on the side of the machine and therefore the lateralend of the conditioning unit. This transmission gearbox generally usesbelts which, in case of overload or even blockage of the conditioningunit, begin to slip on their pulleys. This results in rapiddeterioration of the pulleys, or even a break of the belts, which candamage other parts of the movement transmission line. The corollary ofsuch damage is a significant immobilization time of the machine as wellas high repair costs.

This type of overload may occur if a dense bundle of cut plants, astone, a branch or a tree root arrives in the conditioning unit.

In order to reliabilize the movement transmission done by this gearbox,it is interesting to use a gear transmission in that location. However,in order to limit the bulk and cost of such a transmission, oversizingof these gears must be avoided. Using smaller gears makes it necessaryto have a torque-limiting device between that set of gears and theconditioning unit, in order to avoid damaging the gears in case ofoverload of the conditioning unit.

To that end, the invention first proposes to use, in that location, atorque limiter including a shearing element, of the rod type parallel tothe rotation axis.

Nevertheless, the use of such torque limiters has, in this context, amajor drawback, since both for sizing reasons of the parts involved inthe torque transmission and for bulk reasons, it may be delicate, if notimpossible, to access, with the necessary tools, the zone in which it isnecessary to operate to change the shearing element after it has broken.

To that end, the invention proposes to arrange, within the torquelimiter itself, one of the two lockings required to tighten the boltcorresponding to the shearing element.

The invention thus relates to a torque-limiting device for the securetransmission of a rotation between an inlet baseplate and an outletbaseplate that it has, where the torque-limiting device comprises atleast one drive bolt that forms a breaking element by shearing in caseof torque exceeding a predetermined threshold, and where the boltcomprises a nut and a screw and has locking parts.

Such a torque-limiting device is in particular known from document U.S.Pat. No. 4,758,109. On this known device, each baseplate includes arespective hole for the passage of the screw. In one of the baseplates,the head of the screw bears against a shoulder forming the mouthpiece ofthe hole of that baseplate. In the other baseplate, the nut bearsagainst another shoulder forming the mouthpiece of the hole formed inthat other baseplate. The tightening of the bolt between the twoshoulders presses the inlet baseplate and the outlet baseplate againstone another along their rotation axis. The bolt is calibrated to breakwhen the drive torque exceeds the predetermined threshold. However, forthe break of the bolt to actually occur when the drive torque exceedsthe predetermined threshold, it is necessary for the break of the boltto be obtained by its shearing. For this condition to efficiently bemet, it is desirable for one of the holes to have a precise geometryand/or high mechanical characteristics.

It is in particular desirable for this hole to have a diameter that isprecisely adjusted to the diameter of the screw. Precise enoughpositioning of the hole within the baseplate can also be required, whichthen means that at least a large part of the baseplate is produced withfine manufacturing tolerances. It is additionally preferable for thishole to be made in a part of the baseplate having a significanthardness, by means of a material with a hard enough starting grade or bymeans of a subsequent heat treatment. However, on a torque-limitingdevice of the known time, it may not be economically and/or mechanicallydesirable to produce at least a large part, or even all, of thebaseplate with fine manufacturing tolerances, or to make it from a hardmaterial or material subject to a subsequent heat treatment afterpreliminary machining operations. For example, the choice of a hardmaterial grade for the baseplate can complicate the machining operationsperformed in locations of the base other than those where the hole islocated. Furthermore, a heat treatment of a large part or all of thebaseplate following preliminary machining operations generatesdeformations of the part, and therefore subsequent machining re-work. Itmay be considered to produce the hole in an insert having a significanthardness, but this complicates the production of the baseplate as ahole. It is also conceivable to limit the heat treatment of thebaseplate near the hole, however deformations of the baseplate cannot beruled out and can prevent it from being properly coupled with the otherbaseplate.

The present invention relates to a torque-limiting device not having theaforementioned drawbacks. To that end, the torque-limiting deviceaccording to the invention is characterized in that it further has anintermediate baseplate that is driven by the inlet baseplate and whichin turn drives the outlet baseplate, the at least one bolt ensuresdriving of the intermediate baseplate by the inlet baseplate or drivingof the outlet baseplate by the intermediate baseplate, the intermediatebaseplate has at least one locking element by shape cooperation with alocking part of the bolt, i.e., essentially the nut or the head of thescrew of the bolt, to allow it to be mounted with a single screwingtool, of the thin spanner or other type, and the intermediate baseplateassumes the form of two plates pressed against one another in thedirection of the rotation axis of the torque-limiting device, one of theplates is used to house the locking part of the bolt, the other is usedboth for axial support of the locking part and for housing of the screwrod.

It is thus possible to provide materials having different mechanicalproperties and/or to consider more or less precise dimensionalcharacteristics and/or to provide different manufacturing methods, inparticular more or less costly and/or more or less precise, between theinlet baseplate and/or the outlet baseplate on one hand, and the plateson another hand, as well as between the plates themselves. This possibledifferentiation of the material making up these various parts and/ortheir geometric characteristics and/or their manufacturing methods withregard to the mechanical stresses to which those parts are subjected,makes it possible to decrease the cost of the torque-limiting device. Itis in particular possible to provide that the plate used both for axialsupport of the locking part and for housing of the screw rod is madefrom a material and/or according to a manufacturing method developedsuch that the housing has high mechanical characteristics. In the eventof a drive torque exceeding the predetermined threshold, the rod of thescrew is prevented from caulking the inner surface of the housing.Conversely, the other plate including the housing of the locking partwhose shape cooperates with that of the housing can be made from amaterial and/or according to a manufacturing method that is simplerand/or less costly. Indeed, the housing in this other plate essentiallyserves to maintain the rotation of that locking part during mounting anddisassembly operations of the shearing bolt, the mechanical resistanceof that housing can therefore be lower. It is also possible to providethat the passage hole for the screw in the plate both serving for axialsupport of the locking part and for housing of the screw rod is madeprecisely. The screw rod is thus precisely adjusted thereto. In theevent of a drive torque exceeding the predetermined threshold, the rodof the screw is prevented from hammering inside the hole. Conversely,the housing of the locking part in the other plate, the function ofwhich is essentially to maintain the rotation of that locking part, canbe made with less precise manufacturing tolerances. Thus, the inventionallows the passage for the screw rod in a plate to be made preciselyand/or to have a high mechanical strength. This results in bettercontrol of the torque at which the bolt breaks, since the latter isactually stressed in shearing. This advantageous effect is obtained byretaining the possibility of a reduced manufacturing cost of thetorque-limiting device due to the presence of the intermediate baseplateassuming the form of two distinct plates.

The invention also relates to an agricultural machine, in particular tocut and condition plants, having a rotary assembly, in particular forconditioning cut plants, driven by a set of gears. This machine ischaracterized in that it comprises a torque-limiting device as describedabove, mounted between the set of gears at the inlet baseplate and therotary assembly at the outlet baseplate, and sized to avoid damaging theset of gears in case of blockage of the rotary assembly.

The invention will be better understood using the following description,which describes still other advantages and is related to preferredembodiments, provided as non-limiting examples, and explained inreference to the appended diagrammatic drawings, in which:

FIG. 1 is a diagrammatic view of a torque-limiting device according tothe invention;

FIG. 2 is a perspective view of a first embodiment;

FIG. 3 shows a torque-limiting device that is partially disassembled;

FIG. 4 shows a torque-limiting device according to a second embodiment;

FIG. 5 is a sectional view of a torque-limiting device according to theinvention;

FIG. 6 shows the inside of the transmission gearbox, and

FIG. 7 shows an agricultural machine including a torque-limiting deviceaccording to the invention.

The invention therefore relates to a torque-limiting device (1) for thesecure transmission of a rotation between an inlet baseplate (2) and anoutlet baseplate (3) that it has, where the torque-limiting device (1)comprises at least one drive bolt (5) that forms a breaking element byshearing in case of a torque exceeding a predetermined threshold, andwhere the bolt (5) comprises a nut and a screw and has locking parts.The locking parts are used to tighten by screwing and thereforepreferably assume the form of a nut and a screw head with hexagonalshapes.

The bolt (5) thus participates in transmitting the torque from the inletbaseplate (2) to the outlet baseplate (3) and shears for thattransmission. The bolt (5) therefore takes up its position parallel tothe rotation axis. The inlet baseplate (2) is driven by an elementoutside the torque-limiting device (1), and the outlet baseplate (3) inturn drives a downstream part. The torque-limiting device (1) is thusmounted in a kinematic chain between an upstream part, fastened to theinlet baseplate (2), and a downstream part, fastened to the outletbaseplate (3).

The invention is in particular characterized in that the torque-limitingdevice (1) further has an intermediate baseplate (4) that is driven bythe inlet baseplate (2) and that in turn drives the outlet baseplate(3),

the at least one bolt (5) ensures the driving of the intermediatebaseplate (4) by the inlet baseplate (2) or the driving of the outletbaseplate (3) by the intermediate baseplate (4),

the intermediate baseplate (4) has at least one locking element by shapecooperation with a locking part of the bolt (5), i.e., essentially thenut or the head of the screw of the bolt (5), to allow it to be mountedwith a single screwing tool. The inlet baseplate (2) and the outletbaseplate (3) are therefore not directly engaged with one another, butby means of an intermediate baseplate (4), set in motion by the inletbaseplate (2) and setting the outlet baseplate (3) in motion. Theshearing bolt (5) can naturally be provided between the intermediatebaseplate (4) and the inlet baseplate (2) or between the intermediatebaseplate (4) and the outlet baseplate (3). FIG. 1 shows the secondpossibility.

The invention proposes to arrange, at the heart of the intermediatebaseplate (4), a housing the geometric shape of which makes it possibleto lock part of the bolt (5), preferably its nut, in rotation. Thus, oneonly has to act on the other locking part of the bolt (5), i.e.,preferably the screw head, to successfully tighten the bolt (5)correctly. It is therefore not necessary to have access to both ends ofthe bolt (5); instead, access to only one end suffices, namely the endbeside the inlet baseplate (2). The advantage of providing shapecooperation with the nut rather than the screw head in the intermediatebaseplate (4) is, as will be described later, that it is then possibleto consider leaving a nut in a cavity of the intermediate baseplate (4).

It is more advantageous to provide shape cooperation in the intermediatebaseplate (4) with the nut as locking part than with the head of thescrew as locking part.

For the locking part that will be engaged in the intermediate baseplate(4), it is more advantageous to choose the nut of the bolt (5) than tochoose the head of the screw. Indeed, it is then possible to leavecompletely unused nuts in the intermediate baseplate (4), without thembeing damaged after the shearing bolt (5) breaks, by the rotation thatappears between the intermediate baseplate and the baseplate to whichthe bolt (5) fastens it.

Thus, the locking element preferably assumes the form of a hexagonalhousing (6), in which the locking part can be placed.

Furthermore, it may be advantageous to position the at least one bolt(5) closer to the rotation axis of the torque device (1) than thefastening provided for the intermediate baseplate (4) to set it inmotion via the inlet baseplate (2) is positioned. With thisconfiguration, it is in fact difficult to have access to both ends ofthe bolt (5), since one of them is concealed by the inlet baseplate (2),with larger dimensions than the intermediate baseplate (4).

FIG. 1 shows a fastening of the intermediate baseplate (4) on the inletbaseplate (2) using screwing. Taking into account the function forprotecting against excessive torque that must be performed by the bolt(5), calibrated, the fastening between these two baseplates is of coursecapable of transmitting a higher torque than that at which the bolt (5)breaks. FIGS. 2 to 5 show, however, that the fastening of the inletbaseplate (2) on the intermediate baseplate (4) is done by screwsengaged in the intermediate baseplate (4) itself, whereas FIG. 1illustrates a nut.

The invention is also characterized in that the intermediate baseplate(4) assumes the form of two plates (7, 7′) pressed against one anotherin the direction of the rotation axis of the torque-limiting device (1),

one of the plates (7′) serves as the housing for the locking part of thebolt (5), namely the nut or the head of the screw, and the other (7)serves both as axial support for the locking part as well as for thehousing of the screw rod. It is thus possible to provide materialshaving different mechanical properties and/or to consider more or lessprecise dimensional characteristics and/or to provide differentmanufacturing methods, in particular more or less costly and/or more orless precise, between the inlet baseplate and/or the outlet baseplate onone hand, and the plates on another hand, as well as between the platesthemselves. This possible differentiation of the material making upthese various parts and/or their geometric characteristics and/or theirmanufacturing methods according to the mechanical stresses to whichthose parts are subjected, makes it possible to decrease the cost of thetorque-limiting device. It is in particular possible to produce thepassage for the screw rod sufficiently precisely on a plate and/or tomake that plate from a material having high mechanical characteristics,so as to have good control of the shear resistance. It is also possibleto produce the locking element in another plate, with less precisedimensional characteristics and/or with a simpler and/or less expensiveand/or less precise manufacturing method. FIG. 5 shows that the screwrod of the bolt (5) crosses through the outlet baseplate (3) as well asone the plates (7), then emerges in the locking element arranged in theother plate (7′). The nut, located in the locking element, arrivesagainst the other plate (7), following the tightening of the screw headof the bolt (5).

According to one possible additional feature, the bolt (5) is mountedbetween the intermediate baseplate (4) and the outlet baseplate (3),which provides easier access to the head of the screw from the outsideof the torque-limiting device (1). Thus, if the bolt (5) breaks inconsidering the resistance of the element driven by the outlet baseplate(3), the intermediate baseplate (4) continues to rotate and the outletbaseplate (3) is stationary. It is then advantageous to provide alubricant between the contact surfaces of the two baseplates, so as toavoid excessive wear generated by the rotation of only the intermediatebaseplate (4) after the bolt (5) has broken before the end of therotation of the inlet baseplate (2).

According to another possible additional feature, the torque-limitingdevice (1) has a larger number of locking elements than of bolts (5),the torque-limiting device (1) in particular having a single completebolt (5) and a plurality of locking elements. Advantageously, a nut isprovided in at least one locking element other than that cooperatingwith the at least one bolt (5), in order to be able to tighten athreaded rod therein to form another bolt (5), without a majordisassembly operation. A nut is in particular provided in each lockingelement other than that cooperating with the at least one bolt (5).Thus, when the bolt (5) breaks, it suffices to install screws in thecorresponding nuts. It is only once all of the nuts are engaged bybroken threaded rods that it is necessary to disassemble thetorque-limiting device (1) to remove them and replace them with a newset of nuts, then next a screw to form a new bolt (5).

In specific embodiments, and according to one possible additionalfeature, the locking elements are positioned relative to one another sothat when a bolt (5) is engaged in one of them, at least one otherlocking element is not accessible, while in particular being covered bythe outlet baseplate (3), which then only has the number of orificesnecessary to leave passage to the number of bolts (5) corresponding tothe sizing of the maximum transmissible torque. Thus, it is not possibleto increase the maximum transmissible torque by installing more bolts(5) than provided. Increasing the maximum transmissible torque may infact lead to breaking another element of the kinematic chain, up to theconditioning device. FIGS. 2 and 3 show that, when the set of boltsconsidered for the maximum transmissible torque is in fact assembled,the outlet baseplate (3) prevents access to the other locking elements,where a locking part is found each time, preferably a nut, to formanother bolt (5) in case of break.

In specific embodiments, in particular illustrated in FIG. 4, at leastone locking element emerges at the circumferential surface of theintermediate baseplate (4), such that it is possible to insert, from theside, one and/or the other of the elements of a bolt (5), namely the nutand/or the screw. In the case of FIG. 4, the intermediate baseplate (4)is arranged so that both the nut and the screw can be brought from theside. In absolute terms, such a locking element emerging at thecircumferential surface of the intermediate baseplate (4) can convergeon the side only to allow a nut to pass, or only to allow a screw topass. The advantage of such a construction is of course facilitating thechanging of broken parts after a bolt (5) has broken.

Lastly, according to another possible additional feature, thetorque-limiting device (1) has an engine's side (8), and the inletbaseplate (2) has screw passage orifices for fastening the baseplate toa driving rotary element positioned on the engine's side (8). Thedriving of the torque-limiting device (1) therefore takes place from theengine's side (8), the rotary assembly (9), in particular forconditioning, driven by the torque-limiting device (1) also beinglocated on the engine's side (8). Thus, the side opposite thetorque-limiting device (1) is accessible for the various necessarymaintenance operations. Thus, the intermediate baseplate (4) is pressedagainst the inlet baseplate (2) and fastened to the latter by screwingaccessible for unscrewing from the engine's side (8), as in particularshown in FIG. 5. This figure also shows that the intermediate baseplate(4) is caught between the inlet baseplate (2) and the outlet baseplate(3), and that the outlet baseplate (3):

-   -   is fastened to the intermediate baseplate (4) by the at least        one bolt (5) accessible for unscrewing from the side opposite        the engine's side (8),    -   extends in the direction of the engine's side (8) at a bush that        the outlet baseplate (3) has and which is located at least at        the heart of the intermediate baseplate (4) in a central        orifice, that the intermediate baseplate (4) has to that end,        indeed also at the heart of the inlet baseplate (2) in a central        orifice that the inlet baseplate (2) also has to that end. The        bush is in particular fluted over its inner circumference to        drive an output shaft that will be inserted therein.

The invention also relates to an agricultural machine, in particular forcutting and conditioning plants, having a rotary assembly (9), inparticular for conditioning cut plants, driven by a set of gears (10),the set in particular being placed within a lateral gearbox (11), placedon the side of the machine to bring a torque to the rotary assembly (9).It may preferably involve a machine for cutting and conditioning plants,as shown by FIG. 7, designed to be driven by a tractor.

According to the invention, this machine comprises a torque-limitingdevice (1) for the secure transmission of a rotation between an inletbaseplate (2) and an outlet baseplate (3) that it has, where thetorque-limiting device (1) comprises at least one drive bolt (5) thatforms a breaking element by shearing in case of a torque exceeding apredetermined threshold, and where the bolt (5) comprises a nut and ascrew and has locking parts.

Furthermore, the torque-limiting device (1) is mounted between the setof gears (10) at the inlet baseplate (2) and the rotary assembly (9) atthe outlet baseplate (3),

and sized to avoid damaging the set of gears (10) in case of blocking ofthe rotary assembly (9). Such a torque-limiting device (1) thereforeoperates with a breaking element shearing in the transmission of thetorque up to the rotary assembly (9).

The torque-limiting device (1) may also have one or several of thefeatures described above. Thus, in certain specific embodiments of theagricultural machine, the torque-limiting device (1) that it hasupstream from the rotary assembly (9) further has an intermediatebaseplate (4) that is driven by the inlet baseplate (2), which in turndrives the outlet baseplate (3),

the at least one bolt (5) ensures the driving of the intermediatebaseplate (4) by the inlet baseplate (2) or the driving of the outletbaseplate (3) by the intermediate baseplate (4),

the intermediate baseplate (4) has at least one locking element by shapecooperation with a locking part of the bolt (5), i.e., essentially thenut or the head of the screw of the bolt (5), to allow it to be mountedwith a single screwing tool.

In the embodiment illustrated in FIG. 2, the torque-limiting device (1)has an inlet baseplate (2) in the form of a plate set in motion owing tothe rotation transmitted from the tractor. The inlet baseplate (2) isthus fastened by screwing to the upstream part of the kinematic chain,and to that end has through holes. The head of a screw placed in one ofthese holes remains accessible once the torque-limiting device (1) isnormally placed on the machine It is therefore completely possible for arepair technician to act on these screw heads from the outside todisassemble the torque-limiting device (1).

The torque-limiting device (1) also has an intermediate baseplate (4),fastened by screwing to the inlet baseplate (2). FIG. 2 shows that inthis embodiment, the intermediate baseplate (4) essentially assumes theform of a star with as many branches as there are fastening screws tothe inlet baseplate (2), here three, regularly spaced apart. Theintermediate baseplate (4) is fastened by screwing to the inletbaseplate (2), at through holes of the inlet baseplate (2). The screwsare then preferably mounted such that the heads are located on the sideof the inlet baseplate (2), which makes it possible to avoid erroneousdisassembly. The intermediate baseplate (4) is essentially made up oftwo plates (7), (7′), identical in shape and pressed against oneanother. The interest of using two plates rather than a one-pieceintermediate baseplate (4) will also be described below.

The torque-limiting device (1) also comprises an outlet baseplate (3),which assumes the form on one hand of a plane portion, fastened to theintermediate baseplate (4) and against it, the intermediate baseplate(4) being in that location between the inlet baseplate (2) and theoutlet baseplate (3), and on another hand a bush shaped portion thatextends inside the torque-limiting device (1), from the plane portiontoward the inlet baseplate (2). With such a construction, it is possibleto arrange a torque limiter whereof the inlet driving and the outletdriving are on the same side, which makes one face of thetorque-limiting device (1) completely accessible. The outlet baseplate(3), at its plane portion, is fastened to the intermediate baseplate (4)by at least one bolt (5), the head of the screw of which is shown byFIG. 2. Such a bolt (5) is traditionally made up of a screw and a nut,and it is preferably the hexagonal head of the screw that is accessiblefrom the free face of the torque-limiting device (1). The bolt (5) thusforms the torque-limiting element, shearing at the rod of its screw. Infact, the rod of its screw therefore extends on one hand in the planepart of the outlet baseplate (3), and on another hand in theintermediate baseplate (4), crossing through one (7) of the two plates.The shearing force experienced by the rod of the screw of the bolt (5),and which generates breaking in case of excessive torque, is thereforesituated in the plane separating the outlet baseplate (3) on one handand the intermediate baseplate (4) on another hand.

The head of the screw of the bolt (5) constitutes a locking part, owingto an outer hexagonal shape, compatible with a thin spanner, or an innerhexagonal shape, compatible with a key of the Allen type. The head ofthe screw thus emerges outside the outlet baseplate (3), to becompletely accessible from the free side of the torque-limiting device(1). The other locking part of the bolt (5) essentially consists of ahexagonal nut. This nut is engaged in the intermediate baseplate (4), ina cavity with a corresponding shape, to avoid the rotation thereof. Theintermediate baseplate (4) thus ensures the rotational maintenance ofthe nut, such that the simple maneuvering of the head of the screwsuffices to tighten the bolt (5) and firmly secure the intermediatebaseplate (4) to the outlet baseplate (3).

It is therefore necessary to guarantee good maintenance of the threadedrod of the bolt (5) in the intermediate baseplate (4), so as toguarantee that the break occurs effectively by shearing, and to be ableto calibrate the bolt (5) accordingly.

Producing the intermediate baseplate (4) in the form of two plates (7,7′), one against the other, then makes it possible to provide one formaintaining the rod of the screw of the bolt, to guarantee the shearingstress, and to provide another to maintain the nut in rotation. Theadvantage of producing the intermediate baseplate (4) in two plates (7,7′) is then to be able to use different materials, in particular more orless sophisticated, and/or with different mechanical strengths, and/ordifferent manufacturing methods, in particular more or lesssophisticated and/or more or less precise, for the purpose of arranginga passage for the screw rod in one plate, and a cavity for the nut inthe other plate.

FIG. 5 also shows that, once the bolt (5) is tightened, the nut, housedin one (7′) of the two plates, comes into contact with the other (7),which makes it possible to produce the cavity for the nut with aconstant section. Once the intermediate baseplate (4) is mounted on theinlet baseplate (2), the nut is no longer accessible, only the head ofthe screw is still accessible.

The star configuration of the intermediate baseplate (4) is used againat the outlet baseplate (3), since, as shown by FIG. 2, the bolt (5) isprovided in one of the component branches of the intermediate baseplate(4). The bolt (5), the rotation axis of the torque-limiting device (1)and a fastening screw of the intermediate baseplate (4) on the inletbaseplate (2) are therefore aligned. Other geometric configurations areof course possible.

It should also be noted that, although FIG. 2 shows a torque-limitingdevice (1) with a single bolt (5), it is conceivable that several bolts(5) can be mounted simultaneously.

FIG. 3 shows another advantageous aspect of this embodiment. Theintermediate baseplate (4) has a plurality of housings for nuts, a nutbeing housed in several of them. It is thus possible to leave at leastone unused nut at the heart of the intermediate baseplate (4). After thescrew rod of the complete bolt (5) is broken, it will then suffice toinstall a new screw rod in another nut, without necessarily releasingthe entire nut in which part of the broken rod is still housed. FIG. 2shows that the unused nuts are not accessible, which avoids thesimultaneous mounting of an excessive number of bolts (5), which wouldresult in providing less protection for the gear.

Owing to the provision of a plurality of cavities for nuts and,furthermore, at least one unused nut, repairs are very simple sinceafter breaking, it suffices to remove the detached part of the bolt (5),shift the outlet baseplate (2) until the screw hole is opposite a nutpresent in the intermediate baseplate (4), then insert a screw thereinto form a new bolt (5). The intermediate baseplate (4) therefore alsoforms a prefilled loader to form a new bolt (5) quickly. After severalsuccessive breaks, when all of the nuts of the torque-limiting device(1) have been used, it will then be necessary to separate theintermediate baseplate (4) from the inlet baseplate (2), so as to beable to dislodge the nuts, part of the rod being screwed therein.

FIG. 4 shows a second embodiment of the invention, which facilitates thechanging of the nut. After the screw rod is broken, in the planeseparating the outlet baseplate (3) and the intermediate baseplate (4),it may be advantageous to be able to replace both parts of the bolt (5)separated by the break right away, namely part of the screw on one hand,and a nut with the rest of the screw on another hand.

FIG. 4 shows that the cavity in which the nut is housed, as well as thecavity that crosses through the screw, emerges on the side of theintermediate baseplate (4), at its outer circumference. Thus, theplacement or removal of a nut is not done from the rear of thetorque-limiting device (1), i.e., from the side of the inlet baseplate(2), but actually from the side of the intermediate baseplate (4). It isthus possible, after the break, to laterally remove the nut and the partof the screw engaged therein, then to put in a new screw from the side,and lastly to engage a new threaded rod to form a new bolt (5).

FIG. 6 shows the set of gears (10) located in the gearbox. This figureshows that the inlet baseplate (2) is located against the last, lowestgearwheel, the outlet baseplate (3) is located at the other end of thetorque-limiting device (1). The gearwheel against which thetorque-limiting device (1) is situated is therefore located, relative tothe torque-limiting device (1), on the same side as the shaft that thetorque-limiting device (1) drives downstream. On the other side of thetorque-limiting device (1) is its accessible part, from whichmaintenance operations can be carried out. The figure illustrates thatthe disassembly of the torque-limiting device (1), and above all thedisassembly of the bolt (5), can both be done from the same side. Italso illustrates that the intermediate baseplate (4) is placed directlyagainst the inlet baseplate (2), but also that the bolt (5) is notlocated at the periphery both of the intermediate baseplate (4) and ofthe inlet baseplate (2), which prevents easy access to the nut from therear. Without recourse to the invention, if the bolt (5) breaks, itwould be necessary to separate the torque-limiting device (1) from thewheel on which it is mounted, which is possible owing to the screw headsemerging in the front part, then to next separate the inlet baseplate(2) from the intermediate baseplate (4), owing to the access obtained tothe heads of the fastening screws with respect to one another, then tochange the nut.

With a torque-limiting device (1) according to the invention, thereplacement of the breaking parts is very easy, the torque-limitingdevice further having a small bulk. The use of a general torque-limitingdevice by shearing to protect the rotary assembly, in particular forconditioning, of an agricultural machine makes it possible toreliabilize the transmission and reduce its bulk.

Of course, the invention is not limited to the embodiments described andshown in the appended drawings. Modifications remain possible, inparticular regarding the composition of the various elements, bydifferent combinations of all or part of the features described above,or by substituting technical equivalents, without going beyond the scopeof protection of the invention.

The invention claimed is:
 1. A torque-limiting device for secure transmission of a rotation between an inlet baseplate and an outlet baseplate, the torque-limiting device comprising: one drive bolt that forms a breaking element by shearing in case of a torque exceeding a predetermined threshold, and wherein the bolt comprises a nut, a screw, and locking parts; an intermediate baseplate that is driven by the inlet baseplate and that in turn drives the outlet baseplate, the intermediate baseplate positioned in between the inlet baseplate and the outlet baseplate so that the inlet baseplate is spaced apart from the outlet baseplate; the bolt ensures driving of the intermediate baseplate by the inlet baseplate or the driving of the outlet baseplate by the intermediate baseplate; the intermediate baseplate comprises one locking element by shape cooperation with a locking part of the bolt, the nut,or head of the screw of the bolt, to allow it to be mounted with a single screwing tool; and the intermediate baseplate comprises two plates pressed against one another in the direction of the rotation axis of the torque-limiting device, one of the plates serves as a housing for the locking part of the bolt, the other serves both as axial support for the locking part and for housing of the screw rod.
 2. The device according to claim 1 wherein the bolt is mounted between the intermediate baseplate and the outlet baseplate.
 3. The device according to claim 1, wherein the locking element emerges at a circumferential surface of the intermediate baseplate, such that it is possible to insert, from a side, the nut and/or the screw of the bolt.
 4. The device according to claim 1, comprising an engine's side, and the inlet baseplate comprises screw passage orifices for fastening the baseplate to a driving rotary element positioned on the engine's side, the intermediate baseplate is pressed against the inlet baseplate and fastened to the inlet baseplate by screwing accessible for unscrewing from the engine's side, and is caught between the inlet baseplate and the outlet baseplate; and the outlet baseplate: is fastened to the intermediate baseplate by the bolt accessible for unscrewing from a side opposite the engine's side, extends in the direction of the engine's side at a bush of an outlet baseplate and which is located at a heart of the intermediate baseplate in a central orifice that the intermediate baseplate has to that end.
 5. An agricultural machine, for cutting and conditioning plants, comprising a rotary assembly, for conditioning cut plants, driven by a set of gears, and comprising a torque-limiting device according to claim 1, wherein the torque-limiting device is mounted between the set of gears at the inlet baseplate and the rotary assembly at the outlet baseplate, and sized to avoid damaging the set of gears in case of blockage of the rotary assembly.
 6. The device according to claim 1, wherein a first of the two plates of the intermediate baseplate is made from a first material, and a second of the two plates of the intermediate baseplate is made from a second material different from the first material. 